I am sorry you are so frustrated. First know that many spend years looking for a diagnosis. MS is very hard to diagnose. White spots can be caused by many many things. Doctors do not want to make mistakes. The current FDA treatments for MS are very expensive injections. Doctors just can't try MS as a diagnosis and see how it goes.
You may want to ask for evoked potentials. It is far less invasive than that (ugh..and boy do I agree there) spinal tap. What they do with evoked potentials is hook you up to electrodes (on your scalp...completely painless) and then they see what your response times are to various stimulations. Most people have hearing, vision and extremeties. I had vision (abnormal), hearing (normal) and lower extremeties (delayed). Along with the MRI this test was very revealing. I also had MS typical reflexes and response to the doctor's neurological exam.
Your symptoms of blacking out and losing time are not at all typical for MS. That may be the reason your doctor is still looking at your head injury. And again, the problem with MS symptoms is that so many other diseases/ illnesses and health conditions have those very same symptoms.
Good luck. I truly hope you don't have this disease. Below is a very good site discussing the diagnostic process for MS.
Gretchen ~ diagnosed with MS July 2006
I have no lesions on my soul and so I will live with no limits.